Well... I'm seeing a bit of problems with your builds.

It seems you are wanting to do more than PVE, so that requires you to spec differently.

All my specs are around this.

And I can tank just fine. Also, when I do 10 mans, I keep them in Tank gear and they can dps fine, I was pulling 1700+ while tanking. Of course, that is multiple mobs attacking me.
When it comes to DK's and Boxing, you are going to need them to all be tanked out. I tried making my alts dps, and I got worked on trash. Though, now I have healers getting closer to my level, so I will be able to run with a healer and 4 dks if I want, but I'm still going to keep them tanked spec.

If I can clear Heroics with 5 tanks, then, yeah, you with 4 and a healer will do just fine.

I might be able to downgrade my gear to what it was before I started getting decent gear then run HOL again and record it.
I was doing it with only 2-3 being 540 defense, and the others around the 520ish to 530ish.

The Stacking Blood Aura and Rune tap make things so much easier. Specs are going to kill you with DK's. Bld had a hard time finishing the 3rd boss in HOL as well. I had a hard time, till I speced this spec, I NEEDED IBF and VAMP to be together, as soon as I got that, then I was able to clear the 3rd boss.

Pets on that boss are pointless, they are just going to die because of the dot, but they are going to help a little. Since you or, some of your alts have specs that give you pets, they might last a little bit longer. My only need, or want for Unholy is the pet stunning... Round Robin pet stunning makes trash easy as hell.

If you have the funds and the means to make all 4 of them blood/frost, then that might work, or rather it will work.